Sound receiving apparatus



Aug. 18, 1936. w, c EDDY SOUND RECEIVING APPARATUS Original Filed July28, 1932 2 Sheets-Sheet l E c R u m IU N w s 2 6 m T M u w HM H N mINVENTOR William C. Eddy 2% ATT RNEY Aug. 18, 1936. w. c. EDDY SOUNDRECEIVING APPARATUS Original Filed July 28, 1952 2 Sheets-Sheet 2INVENTOR William C. Eddy BY 4Mb-44L u-i 0 I ATTORNEY Patented Aug. 18,1936 UNITED ST TES PATENT OFFICE Original application July 28,1932,Serial No.

625,501. Divided and this application Angus 22, 1934 Serial No. Moss 6Claims. (Cl. rut-sac) (Granted under the act of March 3, 1883, asamended April 30, 1928; 370 0. G. 757) This invention relates to soundreceiving apparatus, more particularly to'an amplifier to be used inconnection with an electric sound ranging compensator, and is a divisionof my application Serial No. 625,501 flied July 23, 1932.

The principal object of this invention is to provide a system whereinthe direction of a source of sonic signals may be determined bycombining the sonic signal controlled currents set up in a plurality oflinearly displaced microphones or sound receivers in such a manner thatthe resultant combined current rises to a sharp maximum when theplurality of microphones or sound receivers are effectively focussed onthe source of sonic signals.

A second object is to eliminate the necessity for the diflicult trainingof binaural listeners by improving directiondetermination by a combined.maximum and minimumindicatlon.

A third object is to reduce the background of noise and to improve thesharpness of the maximum indication by the use of audio tuning thatpermits the use of the higher frequency components of the sound source.

A fourth object is to provide a visual means to indicate the properadjustment of the compensator.

The apparatus of this invention is adapted primarily for use with anelectric compensator such as shown in U. S. patent to Pierce No.1,682,712. Briefly, it comprises twelve equally spaced microphones that,by groups of three microphones. are each connected to first retardationlines. The centralmicrophone of each group is connected to a fixedretardation line, the other end of which is movably connected to thefirst retardation line, and the outside microphones of each group areconnected to opposite ends of corresponding first retardation lines. Byadjusting the mov- 40 able connection\of the fixed retardation lines tothe first retardation lines, the electric currents caused by the soundfrom any direction striking each group of three microphones can bebrought into phase at the corresponding movable con- 45 nections. Themovable connections of the forward two groups of microphones areconnected to opposite ends of a second retardation line, and the movableconnections of the after two groups of microphones are connected toopposite ends of another second retardation line. These secondretardation lines have movable connections that may be adjusted so thatthe electric currents from the forward two groups of microphones and theelectric current from the after two groups of microphones mayrespectively be.

brought into phase at their corresponding connections. The movableconnections of the second retardation lines are respectivelyelectrically connected to movable contact blocks associated with a thirdretardation line. These contact 5 blocks divide the third retardationline electrically so that the output of the forward groups. of, twelvemicrophones is connected to one portion, and the output of the aftergroup of twelve microphones is connected to the other portion 10 of thethird retardation line. The corresponding other ends of these portionsof the third retardation line are respectively connected to the left andright telephone receivers. By adjusting these contact blocks, timeretardation is introduced into the current through one of the telephonereceivers in excess of the retardation in the current through the otherreceiver, so. as to bring these currents into phase and to effect aproper binaural setting. The function of the third retardation line,when its two ends are separately connected to the two telephonereceivers, is to bring the maximum sounds from the second retardationlines in the two receivers into phase so as to cause the physiologicalsense of the binaural centering of the sound. However, by connecting thetwo telephone receivers in multiple to the two ends of the thirdretardation line, it may be used to combine the currents so as toproduce a maximum sound in each telephone receiver but without thebinaural sensation. It may be noted that the same position of thecontact blocks on the third retardation line that gives blnauralcentering also gives maximum when the two telephone receivers areconnected in multiple to the two endsof the third retardation line.

In a device of this type the focusing ability varies with the frequencyof the received sound. If the microphones of a 12-unit installation arespaced one foot between units, the intensity of a sound of a-frequencyor 300 cycle/sec falls to onehalf its maximum value when it is 36degrees out of focus; that of a sound of a frequency of 800 cycles/secfalls to one-half its maximum when it is 17 degrees out of focus; andthat of a sound of a frequency of 1200 cycles/sec falls to one-half itsmaximum when it is 8.5 degrees out of focus. This improvement infocusing ability with increase of frequency is limited because of thefact 50 that frequencies whose wave lengths in the medium are less thanthe distance between microphone units pan not be employed in a devicethat depends on the adjustment of phase relation for operation. Thesehigh frequencies result in 55 ambiguous readings because there is no wayto be sure that all microphones are beingcompensated for the same. wavefront. Therefore, the electric compensator is usually designed totransmit all frequencies up to 4000 cycles/sec.

In the past it was believed that no advantage could be gained byamplifying the output'from an electric compensator because the localdisturbing noises were amplified in the same proportion as the soundsitwas desired to hear. Also, in binaural operation it is best to keepdistortion reduced as much as possible and it was impossible to buildamplifiers for both ears that were exactly alike.

The present invention is an efficient amplifier for use with an electriccompensator that sharpens and improves the maximum response by combiningwith it the minimum so as to produce a combined signal that is sharplydirective and readily recognized by the untrained listener. It can bestbe described and understood by reference to the accompanying drawings inwhich Fig. 1 shows a diagrammatic arrangement showing the output of thecompensator being led into an.

amplifier whose input transformers are so connected that the maximum andminimum primaries are connected in parallel, and the secondaries,corresponding to said primaries, are diflerentially connected, thesecond stage of amplification being shown with audio tuning.

Figs. 2, 3 and 4 show graphically the curves of minimum" and maximumamplifier response, singly and in combination, as will be hereinaftermore fully explained.

In directional sound receivers of the binaural compensator type. theintensity of the sound received varies more sharply with a change offocus when the currents from the plurality of microphones are combinedin such a manner as to give a minimum indication-when the system isproperly focused on a sound source than when the currents are combinedtogive a maximum indication when the system is properly focussed. It isthus seen that both the maximum and the minimum methods of combining thesignal om ponents of a binaurally centered sound pick up system havedefinite advantages, the maximum method because of the strong signalavailable, :and the minimum method because of the sharp directivity. Inthe'present system, features of both the/maximum and the minimum systemshave beencombined into a single system so means of conductors 4 and 5 tothe input terminals of one of the delay networks of the com pensator 3,while microphone 2 is connected by means'of conductors 5 and 6 to theinput terminals of another and similar delay network of the compensator3. The compensator 3 may, for example, be similar to that disclosed inFig. 5 ofthe above mentioned Pierce patent in which case the inputconductors 4, I, and. 6 connected to the compensator 3 correspond toconductors "I,

4 l3, and 162, respectively of the Pierce patent and Band pass, low passand high pass filters have been used without much success.

In the operation of this the output leads of the compensator 3 numbered20, 2|, and 22 correspond to the leads 8, 305, and 802, respectively, ofPierce. Transformer 23 has a center tapped primary and is connected byway of conductors 28, 2| and 22 to the output terminais of thecompensator 3 for operation on the minimum response, as shown by thearrows depicting the currents when the compensator is focussed on thesound source. The transformer 24 has two equal primary windings 25 and26 that are differentially connected for operation on the maximumresponse, as also shown by arrows. Transformers 23 and 24 are connected,as shown, in parallel across the output leads 20, 2| and 22 of thecompensator 3. The response curve for 1 transformer 23 will be similarto that as depicted in Fig. 2, wherein the ordinates represent theintensity of the sound and the abscissae represent compensator positionsor apparent positions, and

the response curve for transformer 24 will be similar to that shown inFig. 3, wherein the ordinates and abscissae are the same as in Fig. 2.Since the response as indicated by portions 33 is stronger than thatindicated by porti s 49 and in order to have them approximately neu-'clud'es the primary of the'transformer 40. The 35 secondary of thetransformer 49 is connected to the input electrodes of a furtherthermionic tube:

. amplifier 39. The primary 35 of the audio frequency transformer 34 isconnected in shunt with asecondary of the transformer 40. The secondary36 of the transformer 34 has a tuning condenser 31 connectedthereacross, and the transformer 34 and condenser 31 constitute togetheran audio tuning arrangement 33 for tuning the input circuit of thethermionic amplifier 39. The output circuit of the amplifier 39 includesthe primary of a transformer 4|, the sec-' on'dary of which is connectedto the voltmeter or galvanometer 29 and also the head phones 32.

In operation the minimum 3| and the maximum 4| occur at the same settingof the compensator and they combine to give a response graphicallyillustrated by curve iiiv in Fig. 4. Such combination does not aflectthe maximum response but makes the sides of the maximum peak steeper sothat the peak oi. the response maybe more readily" determined and a moreexact direct indication obtained.

When using the combined maximum and minimum response method with theamplifierof this invention, the output is of suflicient strength topermit the use of visual indicating means for determining the direction.of the source of sound.

This is shown by the voltmeter, on other indicating. device, 29. It canbe used alone or in conjunction with the telephone receivers 32 asshown; Indications as large as nine volts have been had with the apparaus of this invention.

, 'vention it has been found desirable to select a frequency from theparticular sound source which gives a good response and has thelea'stinterference from local or other sounds. This is accomplished byproviding an audio tuning arrangement 33 which is connec ed across thesecondary of the first interstage transformer and covers a frequencyrange approximately from 1,000 to 3,000 cycles/sec. The transformer 34is a shunt trap transformer whose primary 85 has a iairly low impedanceand whose secondary It has afairly high impedance, but of such valuethat with a suitable condenser 31 it can be tuned over the frequencyrange desired. This effectively by-passes frequencies except those forwhich'lhe secondary I6 is tuned by condenser 31.

This invention has proved itself of immense value in actual operation.It has increased the effective listening range of this type of soundreceiver three-fold, has imm'oved the accuracy and reliability of thebearings obtained and has simplified the taking of bearings of soundsources so that an untrained listener with very little in struction canobtain the best bearings the apparatus is capable of producing. Itabandons the binaural effect which requires special training of personsthat are naturally adapted to such work and employs the maximum responseprinciple which is easily recognizable by even the unskilled.

While there has been described the preferred embodiment of my invention,it is desired that it be understood that various changes inconstruction, proportion and arrangement of parts may be made within thescope of the subiolned claims, without sacrificing any of the advantagesof this invention.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmentalpurposes, without the payment of any royalties thereon.

I'claim:

i. In combination with an electric sound ranging compensator of thebinaural output type, a

vacuum tube amplifier including a first transformer having aunidirectionally wound centertapped primary connected to the binauraloutput terminals of said compensator, a second transformer having twoapproximately equal primary windings difierentially connected to saidterminalsinparallelwiththeprimaryofsaidfirst transformer, approximatelyequal secondary windings on each of said transformers, said secings thatare differentially connected, theprimary windings of said secondtransformer being electrically connected in parallel withthe primary ofsaid first transformer to the output of said compensator, thesecondaries of said first and secondtransformers being difierentiallyconnected, means for adjusting the value of the input current to saidfirst transformer, and at least one stage of tuned audio amplificationthe input circuit of which is connected to be energized by thesecondaries of said transformers and the output receivers iscombined insuch phase as toproduce.

an alternating current of maximum intensity when said plurality of soundreceivers are eifectively focused on a source of sound, the method ofsharpening the directive characteristics of said 10- system whichcomprises combining a portion of the ouimut current of each of saidlinearly disposed sound receivers to produce an alternating current ofminimum intensity when said sound receivers are effectively focussed ona source of sound, then combining said currents of maximum andminimumintensitlesin phase opposition and utilizing the resultantcurrent to control a signaling means.

4. In combination with an electric compensatcr of the binaural outputtype, an amplifier comprising a first transformer having aunidirectionally wound center-tapped primary winding that-iselectrically connected to the output of ssidto a second transformerhaving two approximately equal primary windings that are differentiallyconnected to the output of said compensator, the secondaries of saidfirst and second transformers being differentially connected; means foradjusting the value of the input current to said first transformer, andat least one stage of audio amplification connected to be energized bythe secondaries of said transformers.

5. In combination with an electric compensator of the binaural outputtype. an amplifier comprising a first transformer having aunidirectionally wound center-tapped primary winding that iselectrically connected to the output of said compensator, a secondtransformer having two approximately equal primary windings that aredifferentially connected to the output -of said'comr, the secondaries ofsaid first and second transformers being difierentialb connected; meansfor adjusting the value of the 4 input current to said firsttransformer, and at least one stage of tunedaudio amplification, saidfirst and second transformers and the transformers of the amplificationstage having fiat frequency response curves over the range offrequencies to be used.

6. A vacuum tube amplifier for combining and amplifying the output of acompensator of the binaural output type a first transformer having aunidirectionally wound centertapped primary winding adapted to beconnected 1 .to the output terminals of.said compensator, a

second transformer having two approximately equal primary windingsdifferentially connected pal-sud with theprimary winding ofsaid firsttransformer, said first and said second transformer having approximatelyequ l secondary windings, an amplifier having input and output circuitsand means for differentially connecting said secondary windings irytheinput circuit of said ,amplifieri WILLIAM EDDY.

